The present invention relates to a magneto-optical head, and in particular, to a magneto-optical head employing a birefringent polarizer composed of crystallines.
Recording and reproducing on a magneto-optical disk are carried out through detection of changes in polarization conditions of an incident light, as widely known. In this case, it is normal that a Wollaston prism shown in FIGS. 7 and 8 is used or 3-beam-separation Wollaston prism shown in FIGS. 9 and 10 is used as a magneto-optical head employing a birefringent polarizer wherein at least two crystallines are cemented (See Japanese Patent Publication Open to Public Inspection No. 187441/1988 (hereinafter referred to as Japanese Patent O.P.I. Publication)).
In the magneto-optical head shown in FIGS. 7 and 8, a laser beam having a linearly polarized light is collimated by collimating lens 2 and passes through polarization beam splitter 3, then, projected on a recording surface of magneto-optical disk D by objective lens 4'. Reflected light subjected to changes in polarization conditions in accordance with recording information of the magneto-optical disk D is passed through the objective lens 4', deflected from its incident light path by the polarization beam splitter 3, subjected to rotation by 45.degree. of its direction of linearly polarized light by half-wave plate 5, passed through condenser lens 6 and cylindrical lens 7, and then divided by the Wollaston prism 8 into first and second beams B1 and B2 which change their intensities in phases opposite to each other in accordance with their polarization conditions. The beams B1 and B2 enter photodetector 9' that is provided with photodetecting elements 91' and 92' which receive the beams B1 and B2 respectively. Thereby, information recorded on the magneto-optical disk D is detected through a difference of output between photodetecting elements 91', and 92' and focusing error signals and tracking error signals are detected through output of the photodetecting element 91'. An illustrated example shows that detection of focusing error signals is carried out in an astigmatism method by means of the condenser lens 6 and the cylindrical lens 7, while detection of tracking error signals is carried out in a push-pull method.
In the magneto-optical head shown in FIGS. 9 and 10, light is reflected from the magneto-optical disk D and deflected from its incident light path by the polarization beam splitter 3 in a manner similar to the aforementioned conventional example. The light passes through condenser lens 6 and cylindrical lens 7 and is divided by the Wollaston prism 8 of a 3-beam-separation type into first and second beams B1 and B2 which deviate to both sides and change their intensities in phases opposite to each other in accordance with their polarization conditions and into third beam B3 which advances along the center and without changing intensity in accordance with polarization conditions. The beams B1, B2 and B3 enter photodetector 9" provided with photodetecting elements 91", 92" and 93 which respectively receive the beams B1, B2 and B3. Thereby, information recorded on the magneto-optical disk D is detected through a difference of output between photodetecting elements 91" and 92", and focusing error signals and tracking error signals are detected through output of the photodetecting element 93". An illustrated example also shows that detection of focusing error signals is carried out in an astigmatism method, while detection of tracking error signals is carried out in a push-pull method.
An optical system in the conventional example mentioned above requires expensive polarization beam splitter 3 in addition to birefringent polarizer 8, and separate optical parts for generation of astigmatism such as a cylindrical lens and other parts. This optical system of an magneto-optical head has disadvantages, because it is large in size and expensive.